This application claims the priority of German application 198 53 410.8, filed in Germany on Nov. 19, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for determining the throttle valve angle in which the throttle valve position is determined by means of a throttle valve model from a rate of air flow and a differential pressure across the throttle valve.
In the case of throttled engines, a throttle valve model is conventionally used in the engine timing system for the model-type description of the throttle valve position. This throttle valve model is usually established from the supercritical rate of air flow through the throttle valve and a reduction factor calculated at an uncritical differential pressure. The inverting of the throttle valve model permits a determination of the throttle valve angle from a predetermined rate of air flow as well as a differential pressure across the throttle valve.
The disadvantage of the above-mentioned approach is the lack of precision in the range of differential pressures between 50 and 100 mbar. At differential pressures lower than 50 mbar, a throttle valve determination from the above-mentioned model can no longer be made in a meaningful manner.
It is an object of the invention to provide a method for determining the throttle valve angle, in the case of which a throttle valve position is also possible at low differential pressures.
This object is achieved by means of an apparatus and method, wherein the throttle valve model is determined from an undercritical rate of air flow through the throttle valve and contains at least two characteristic diagrams, the first characteristic diagram indicating at least two characteristic curves which describe the relationship between the throttle valve angle and the rate of air flow at different differential pressures, and the second characteristic diagram indicating a non-linear transition between the characteristic curves existing in the first characteristic diagram.
In this case, it is important for the invention that another throttle valve model is used which was determined by using as the basis an undercritical rate of air flow. The rate of air flow may be determined from the torque requirement. According to the invention, two characteristic diagrams are used, the first of which containing at least two characteristic curves which describe the relationship of the throttle valve angle with respect to the rate of air flow at different differential pressures, and the second characteristic diagram indicating the non-linear transition between the characteristic curves present in the first characteristic diagram.
By means of the present invention, the required throttle valve angle can be set at any load and rotational speed as well as desired differential pressure. Such a precise and controlled adjustment is required particularly also for rinsing an activated carbon filter.
The differential pressure can be determined by way of a characteristic diagram or from the tank ventilation demand.
When determining the rate of air flow by way of the throttle valve, the rate of air flow by way of a tank ventilation valve is preferably also taken into account and the throttle valve is correspondingly closed when the tank ventilation valve is opened.
In addition, system errors, such as leakage air errors, mechanical tolerances of the throttle valve and errors of the electric throttle valve position detection can also be recognized and can be used in the form of an adaptation for correcting the throttle valve angle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.